Heat insulating materials and method of making



May 10, 1949.

L. H. D. FRASER HEAT INSULATING MATERIALS AND METHOD OF MAKING FiledApril 24, 1945 2,469,379 C -v j Patented May 10, 1949 XANENER HEATINSULATING MATERIALS AND METHOD OF MAKING Lewis H. D. Fraser, Toledo,Ohio, assignor to Owens-Illinois Glass Company, a corporation of OhioApplication April 24, 1945, Serial No. 589,971

7 Claims. (Cl. 106-86) This invention relates to a new type of heatinsulating materials and to improved compositions and methods for theirpreparation.

In the art of making and using insulating materials, and especially inheat insulation for the conservation of high temperatures, it isnecessary to provide a high temperature material for those areas wherehigh temperatures prevail, i. e., above 600 F. But such high temperatureinsulating materials have other characteristics. Thus, they aregenerally of high density and accordingly heavy. Moreover, they areusually not form-retaining or their heat conductivity is higher thanwould be desirable. The cost is also comparatively high.

A sunicient thickness of such high temperature insulation material couldbe employed, so as to insulate high temperature surfaces. But this isnot done. It is generally conceded that it would entail too great aweight of insulation, too

thick a covering (with too large an exterior surface for radiation andloss of heat) and too great an expense. Hence, it would constitute agenerally unsatisfactory installation.

It has for these reasons become standard practice in the insulating ofhigh temperature surfaces to apply a high temperature insulationmaterial which will withstand the heat, and of a suiicient thickness sothat the temperature gradient from its high temperature'side to its lowtemperature-side will assure a temperature of 600 F. or somewhat less onthe low temperature side. This temperature is established as a criterionby the upper safe limit of temperature for the low or lower temperatureinsulation materials which are available, such as moulded (85) magnesia.Insulating materials of the lower temperature type have the advantage oflower apparent density, and lower heat conductivity. Conseduently; theyafford a much greater Thus, 75 magnesia tends to calcine` buildings ortowers. Hence, while they are used in such places, special provisionsand constant care are necessary to avoid or prevent their disruption andfailure.

It is therefore an object of the present invention to provide animproved type of insulating materials which may be applied to hightemperature surfaces, which shall be form-retaining, and which shallalso be of low heat conductivity and low apparent density, and of whichthe entire insulation may be composed. It is also an object to providean insulating material which shall be strong when dry and also resistantto moisture, with minimum loss or reduction of its other de sirableproperties. Other objects will appear from the following disclosure.

It has been an underlying concept of the heat insulation art that, quiteapart from the intrinsic heat conductivity of a material, it could berendered of low eiTective conductivity if it contained numerous voids orair spaces, especially if the voids were individually small so thatconvection currents of air set up in them could be neglected, as in nelydivided powders. Such powders have been bonded together, so as to retainthem in shaped forms and dimensions. Numerous heat insulating materialshave also been made of porous materials, either natural or synthetic,having a sponge-like structure. Such a structure is effective to promoteresistance to the free conductivity of heat therethrough. But,

in general, the volume of such bonded powders I and porous wallstructures, compared to the voids or air spaces enclosed by them, isrelatively large. Hence, such insulating materials have a rela.- tivelyhigh apparent density. Evidence of this is aiTorded by the presentstandards in which medium weight heat insulating materials have anapparentdensity of about 20 lbs. per cubic foot, while even light weightheat insulating materials have an apparent density of 14 to 16 lbs. percubic foot. Though the latter have sometimes been made as low as 12 lbs.per cubic foot, it has been only at the sacrifice of some of thestandard requirements, even for low temperature insulation. Hence, suchproducts are applicable for special purposes only.

It has been proposed to use as heat insulating materials various kindsof bers, in Which voids or air spaces are partially enclosed (ratherthan completely occluded) by the intertwined masses of bers. Inemploying this type of heat insulating construction, the result obtainedis limited inherently by the types of bers (such as natural or articial,etc.), and by the steps or procedure necessary to convert them to theconsistency and forms desired. Bonding materials have been required inorder to impart shape to the mass, and retain the shape and/or volume ofthe shaped mass. These have heretofore usually been in a liquid stateand consequently to a large extent defeat the advantages of the brousstructure. The liquid bond tends to nil the voids and spaces between theilbers and to change the character of the solids and voids from that ofa mass of loose bers and narrow capillary air spaces between them tothat of round air spaces occluded by solid separating walls of iiber andbinder. They are, therefore, structurally similar to the bonded powdersand porous wall structures above described, thus adding both weight andincreased heat conductivity to the resulting product.

In general, therefore, it may be said that the insulating materials oftheprignartnfall into several categories based upon their compositionsand physical structure, as follows:

I. There are those which are composed of finely divided separateparticles which tend to pack loosely and occlude large proportions ofair, distributed between them in the form of numerous and more or lesscontinuous thin lms.

For example, in calories per square centimeter per second per centimeterof thickness, lamp black (C=.00007), lime (.00029), magnesia (.00016-.00045), magnesium carbonate (00023-00025), dry sand (.00093), sawdust(.00012), charcoal (.00012), carborundum (.0005), sil-o-cel (.00011).

But since these are loose powders they consequently have noform-retaining value, and hence no compressive or tensile strengthwhatsoever.

II. There are those which are composed of small solid particles, inloosely or closely packed arrangement, and bonded together in thisrelationship by various means, leaving some of the air spaces open.These air spaces serve to impart a lower conductivity of heat withreference to the mass as a whole, compared to the heat conductivitles ofthe solid particles or of the bonding material per se. But the volumesof the air spaces between the loose particles and their individual sizesandshapes are considerably modified by the bonding material used, asabove pointed out. Insulating materials of this type therefore have aconsiderably higher conductivity of heat than the loose, unbondedpowders.

Such insulating materials are as follows:

Magnesia brick .0027-.0072 Carborundum brick .032-.027 Concrete stone.0022

It will be observed that in bonding the particles together, the productis made susceptible of moulding, and upon setting of the bond it isoften possessed of high tensile and compressive strength in the mass,and therefore form-retaining. However, the increase in apparent densityand in heat conductivity is so many times greater than that of the looseparticles, in their unbonded, independent spaced relationship, thattheir utility, as insulation materials, falls into an entirely differentorder of effectiveness.

' III. The third type of insulating materials is that which presents thecellular or vesicular characteristic of structure. Instead of consistingof solid particles, spaced apart by loose packing, or particles more orless bonded in this loose arrangement, they consist Aof a continuoussolid wall or body material in which air is dispersed in the form ofbubbles. These bubbles of air are consequently more or less, orcompletely surrounded or occluded by the solid material.

Such insulating materials are: diatomaceous earth (.00013), plaster ofParis (.0007), flrebrick (00028-0011) infusorial earth pressed bricks(.0003), and chalk (.002).

This type of insulation is characterized by relatively low heatconductivity or high strength, but

not both together. Moreover, these materials are either naturally formedproducts which would require special shaping or are of relatively highapparent density.

In these several types of insulating materials. in which the structureis that (I) of loosely packed, nely divided particles, or (II) of suchparticles bonded together to form an integrated mass, orV (HI) of acontinuous solid, occluding dispersed voids or bubble shaped spacesfilled with gases; the conductivity of the mass as a whole ispredominantly the conductivity of the solid and hence relatively high.Though the air spaces are small they are nonetheless occluded orsurrounded by solids and hence conducive to transmission of heat byconvection of the gases within them, radiation across them, andconductivity around and through their marginal surfaces. Moreover, thefree surfaces of the material, in such form-retaining structures,whether internally or externally spherical, and hence generally concaveor convex in character, will tend to be of dense formation, as aninherent result of the conditions under which they were assembled andintegrated. Their unions in many cases will be generically those whichare typical of formation by the capillary wetting of solids and liquids.

Hence, insulating materials of these types, in acquiring their mouldingand form-retaining properties, and increased tensile and compressivestrengths, have at the same time increased greatly in their heatconductivity and consequently lost greatly in respect of their heatinsulating qualifications. They are also of relatively high apparentdensities, and constructions made of them are correspondingly heavy.

IV. There is also a group of insulating materials which arecharacteristically composed of loose, ilne fibers and which possess avery low heat conductivity, and therefore of high insulating value, forexample:

Asbestos ber (.00019), cork (00072-00013) Cotton wool (.000043), felted(.000033) Eiderdown (.000046), felt (.000087) f Balsam wool (.000093),hair insulation composed of '75% hair and 25% .lute (.000093), 50% hair50% jute (.000089) It is to be observed that these loose fibrous massesare typically of very low heat conductivity. This is attributable to thedispersed, random relationship of the fibers and to the minute, complex,but continuous system of open spaces between the bers which are filledwith air.

Air has a very low conductivity of heat, especially when in smallvolumes which cannot effectively circulate to transfer it by convection,namely .000058 calorie per square centimeter persecond per centimeter ofthickness. But masses of loose bers have no form-retaining capacity andpresent no tensile or compressive strength. On the contrary, they maytend to mat down, even under their own weight, become more dense andvmore highly conductive of heat and less effective for insulation andleaving an uninsulated air space above them.

V. The loose fibrous insulating materials have been made into sheetspossessing some tensile strength, but such sheets are still lacking incompressive strength and form retention. It may be observed that suchfibrous sheet materials present relatively low heat conductivities andhence high insulating values, though, in general, these properties aresomewhat reduced from those of the loose fibers, and the satisfactoryapplication of them in actual practice is limited. For example:

Asbestos paper (.0004.0006) Blotting paper (.00015), felt (.000087),annel Hair cloth felt (.000042) leather cowhide (.00042) Chamois(.00015), Kapok between burlap or paper Eelgrass between kraft paper(.000086), felted cattles hair (.0000895) Flax fibers between paper(.000096) Jute and asbestos fibers felted (.000127) hair and asbestosfibers felted (.000096), flax ber (.000096) Flax ber (.00011), fiax andrye fiber (.00011) Rock wool or glass wool (.00009) These sheetedfibrous materials are also lacking in form-retention and in tensile andcompressive strength. Moreover, with the exception of asbestes, rockwool, mineral wool and glass wool, they are of organic origin and hencedisintegrate or are inflammable at high temperatures. Consequently, theycannot be used where shaped insulation is required, nor at hightemperatures. Furthermore, they are compacted readily by pressure, or bytheir own weight, in the course of time, whereupon their effective heatconductivity rises, and their apparent density also increases, which isundesirable.

VI. Attempts have been made to bond these fibrous materials analogous tothe bonding of granular insulating materials or powders in groups II andIII described above. But the same results and consequences accrue,namely a more solid structure, resulting in a greatly increased apparentdensity of the mass and a'higher effective conductivity of heat. Thesechanges are attributable to a compacting of the fibrous mass in thebonding operations, the introduction of filling materials between theotherwise loosely spaced fibers, and the formation of a wetting meniscusof the bonding material upon and between the adjacent fibers,constituting an occluding wall or membrane in the finished product,which is of a continuous character throughout the volume of the mass andwhich adds both to the weight and to the heat conductivity of the w le.

In accordance with the present invention, a new type of insulatingmaterial is provided which is primarily of inorganic composition andresistant to high temperatures and characterized by l a loose, o enfibrous structure, in which the fibers are randoml arran ed and separatedor s'p''d ft by a'system or? iin gether and form rounded, occludingboundaries to the air spaces. The synthetically formed and crystallizedbers are joined by direct inherent intergrowth of the fibers withthemselves, and by union with other preformed organic fibers, orinorganic fibrous crystals such as asbestos, which are of a similarcharacter and habit.

In the fundamental aspects of this invention it is found that reagentmaterials, and more particularly inorganic reagent materials, which arecapable of reacting to form crystal growths of a fibrous habit, may beinduced or permitted to develop such fibrous forms predominantly, if notexclusively, and completely, by the provision of a condition ofdispersion of the reagents, and by providing commensurately therewith adispersion of pre-formed finely divided fibers or spicules (i. e.,fibers which already possess and/or which develop before or during theirpreparation a. characteristically, finely divided fibrous form ashereinafter more specifically defined), presenting an abundance of free,fine fibrous ends, which are active to serve as centers for theincipient commencement of crystallization of the fiber-forming reagentmaterials and to insure or promote the development of the latter intone, discrete, fibrous, crystalline form.

The pre-formed activating bers or spicules, thus serving as instigatorsof the incipient crystallization of reaction products (which areinherently capable of forming fibrous products) and directives of theirdevelopment in crystalline form, may be organic or inorganic.

In the latter case, if suitably dispersed, the preformed fibers and thesegregating crystals derived from the fiber-forming reagents maycrystallize, inter se, and thus inherently integrate to form acontinuous, but lamentary, dispersed aggregation of spaced brouscrystals.

In the present specification and claims, the cxpression spiculationrefers to a treatment of naturally rous m'terials, such as asbestos, bywhich the bundles in which they are usually found are separatedlongitudinally to a sufficient degree, such that th`e individual fibrousfilaments resulting present cross-sectional dimensions of 1A@ to 3microns, in either width or breadth, at their extremities or throughouttheir lengths. The degree and type to which it may be carried may becontrolled, inter alia, by the fibrous material used, by the type ofapparatus employed, by the. viscosity of the medium in which thetreatment is carried out, by the efficiency of operation attained.

The term as used in this specification and in the claims, designatesfibrous particles (as obtained by the spiculation treatment) which arecharacterized by cross-sectional dimensions at their extremities of 1A()to 3 microns in either width or breadth and which in length may be ofdifferent orders. For example: (A) in the case of complete spiculationof asbestos, in a medium of low viscosity such as air"i`ilt`e aqueoussuspensions, spicules of from 10 to 1000 microns in which the abovenoted dimensions persist throughout their length; (B) in the case ofpartial spiculation of asbestos, as in the beating of the fiber in moreconcentrated aqueous suspensions (of 1% to 10% by weight) in which thespicules are 'typically from 100 to 2000 microns long, usuallyassociated with a small proportion of bers of the order (A): and (C) inthe case of spiculation by a high speed vortex action in a highconcentration of asbestos in a liquid medium (e. g. 1% to 10% by weight,in water) as accomplished in the apparatus shown in Fig. 2`spiculeshaving a small proportion of fibers of lengths of the order (A) and alarger proportion of fibers of lengths greater than 1000 microns, andfurther characterized by frayed or broomed ends, presenting a pluralityof discrete fibrous filaments having individual cross-sectionaldimensions at their extremities, in either width or breadth, of from1A() to 3 microns.

The viscosity of the resulting aqueous suspensions, when compared at thesame concentration of solids present, is a measure of the degree ofspiculation eiected.

As above mentioned, the pre-formed finely divided s iculategl fibers maybe organic in character. n tli's'cas' e. while capable of serving thesame physical purpose of inducing crystallization from their free endsand separate formation and growth into inorganic flbrguscrjystals, theorganic fbers'wil never heles"t in'sich cases, cohesively integrate withthem, in the sense of continuity of inherent physical structure, thoughthey may present a certain degree of` integration by virtue of physicaladhesion therewith and especially at their free ends.

In either of these cases, however, with preformed inorganic or or anicflbers the crystals ormlrig'sT'i'es'lt of reaction of the reagen' is;presen may aso freely grow oge er between themselves at their points ofincipient contact and thus form an integral brous mass, throughout theentire volume of the dispersion in which they are contained. Thestrength of the resulting integrated fllamentary system is thecumulative inherent tensile strength of the crystals themselves, and ofthe organic or inorganic fibers which served as nuclei in the fibrouscrystalline formation.

In either case, the system is one of molecularly dissolved and/orcolloidally dispersed reagents, capable of reacting to form inorganiccrystals of characteristic fine needle shape or fibrous properties andburr-like habit of growth (resembling thistledown clocks) which areinduced selectively ti'undergo such reaction and to develop such 45habit of growth at numerous points (often in clusters of a .circularradial crystal) dispersed separate from each other in threedimensionsfrom which points they are free and maintained free to extendin all directions through the dispersing liquid medium, throughout theperiod of their reaction. Such growth will preferably be impeded only bycontact with similar crystals, forming undersimilar conditions ofinstigation and growth, whereupon they may grow together therewith atthe point of mutual contact. 'I'hey may also contact with the surfacesof the preformed fibers, with which they may grow together (adhesively)at such point or points of contact with them in solid, fibrous crystalformation. In either case of such contact growth the liquid phase, andconsequent viscosities and meniscus formations which attend it, is notpreserved by solidiiication but replaced by the separation of inherentcrystalline growth of the fiber-forming 55 reagents, and usually of agel which subsequently occupies very much less volume.

The predominant feature of the reactive mass, therefore, is that thereagent materials are presented to so many and such definitely dispersedpoints (about which their incipient reaction and subsequent crystalformation may take place) by the dispersed ends of the spiculated beis,that the crystallization and growth of each crystalline fiber issubstantially uni-dimensional and, in

l0 dispersed points of instigation or origin, and kept dispersed duringat least a substantial period of such growth, they will tend to form anely fibrous mass of crystals. These crystals will in- -Y clude a largeproportion of spaces or voids, will unite directly with such points oforigin and bond with other fibrous materials (without inclusions orocclusions of other and diiierent bonding materials, such as adhesivebinders, cohesive fusions, etc.) and develop their individually markedcharacteristics of high tensile and compressive strengths (due to theirhigh ratio of surface to volume and skin effect characteristics), andremain spaced apart by fine, elongate, continuous, capillary spaces,rather than occluded spherical air spaces with solid, opposed, surfaces,and hence manifest a low apparent density, relatively high compressiveand tensile strengths, a low conductivity to heat, and, conversely, highheat insulating properties.-

To this end, it is found that, for example, lime and silical if in nne1ydivided and mutuauyre? active condition such as an agueous solution or4colloidal sus ension, of active or ydra ed lime and d act-ive or h ratedsilica, tend to react, as by tfe direct application of heatand pressurekto form hydrated calcium sili'cwhic able of anv appropriate needleike orfibrous crystal formation.

. In ordinary mixtures of lime and silica (such as 40 for sand-limebricks), the resulting product will ingly promo e The reac on s ni 1a ean But if lime is employed in the form of uic i;

lime, h drated li I, or milk of lime, and pre era ly contairnng a highproportion of active (e. g. sugarsoluble) lime the reaction is increasnac 1v1 y and completeness. If the silica is finely divided, it is morereactive, but its chemical condition is also important. It

ispreferably used in the form of lactive silica, .a

such as diatomaceous earth or h dratedsiliggi. t promoted by Wa s earn,increased ressure, etc., and also y t e condition of the lim's, in thecontrolled hydration of the lime to produce milk of lime of maximumactivity. The reaction of lime and silica can be promoted, in accordancewith the present invention, so as to result in substantially completetransformation of both into a mass of calcium silicate a considerableproportion of which is in the form of discrete, needle-like crystals andof a new molecular form of hydrated calcium silicate. It is now foundthat the distribution of the needleillape orriibmuaform of t11 .rytalscan be promotedA andcontrolled by the presenceof suitably'prelformed,dispersgdspiculated 'as asbestos, papi"'flber"s`,` and the like.Moreovelthercrys a iza on will tend to grow outwardly from such spacedpoints of inception which are presented by the free, and preferablyfreshly fractured ends of the pre-forrned bers,

Thereby the brous crystals formed are dispersed and kept dispersed bytheir own growth, and by the spiculated characteristics of thepre-formed fibers as well as by the water (and steam) in and from whichthey are formed. Upon evaporation of the residual steam and water frombetween the mass of formed and fully crystallized, fine needles, thevoids are occupied by air. (There is also an enormous shrinkage in thegel which is usually formed in the reaction). As a result the mass as awhole will thus contain a considerable volume of air, so that theapparent density may be correspondingly low and considerably less thanthat of heavy, mediunn, or light weight insulating materials heretoforeknown to the art.

The pre-formed flbrous or spiculated" component which is suitable forthus effecting the present invention may, as already stated, be oforganic or inorganic origin or composition, and will have correspondingproperties and utilities accordingly. It is characteristically of acolloidal order of dimensions in its cross-sectional dimensions, namely,from less than 1 to Bmicrons, and

of dimensions in length which considerably dominate the cross-sectionaldimensions, but which are still of small dimensional order, relative tountreated fibers, for example, to 1000 microns, 100 to 2000 microns, orover 1000 microns. Such fibers, therefore, are susceptible of dispersionin a liquid medium such as water and of maintaining such dispersion fora considerable period of time, without appreciable loss of uniformity orspontaneous dewatering or segregation of the liquid therefrom bygravity, on standing.

Such spiculation of asbestos or other fibers to a cross section of lessthan three microns, and lengths of at least three times their diameters,has a certain distribution significance. That is:

Suppose each of the fibers to be just three microns in diarneter and tenmicrons long. They will be able to pack or disperse relative to theirends (which are to act as centers for inducing incipient crystallizationof the calcium hydrosilicate needles, prisms or fibers) in criss-crossfashion. But they are solids and hence any two of these fibers will notcross in the same plane. They will pile up. The distance between thesurfaces of the free ends of these crossed spicules would be about 5microns or a little more. Now the interposition of a third pre-formedber or spicule. in closest three-dimensional random arranged with thefirst two would stand vertically to the first two. Its faces would thenbe spaced about 2 microns or less than the thickness of the fiber fromat least one of the faces of the other two spicules.

Hence with fibers having lengths no greater than about three times theirdiameters. the eX- posed, fractured. and hence crystallization-reactiveand inducing faces will be nearer to each I .other than thecross-sectional dimensions of their a 1% `pu'lpb'r suspension ofspicules in water f by weight) would correspond to a volume percentage,with asbestos of sp. gr. 2.5, of about .4%. That is, in one thousandcubic microns of the suspension (or a cube ten microns on a side) therewould be four cubic 4microns of asbestos which would be equivalent toone asbestos fiber, one micron square and four microns long.

If this fiber were in the middle of its allotted ten micron cube itwould be four and one-half microns away from the cube Wall on each sideand three microns away from the cube wall at each end. Hence it wouldhave an aqueous film of a thickness several times its diameter on eachside and almost equal to its length at the ends. If the next adjacentfibers, in adjacent similar tenmicron cubes of liquid, were similarlyspaced, and parallel to the first, such adjacent bers would be ninemicrons apart at the sides and six microns apart at the ends (orsomething between these values if the spicules were turned about indifferent perpendicular or angular di" rections with respect to eachother).

If the fibers were longer than four microns, there would be less ofthem, of course, in a 1% suspension.

Likewise if they were bigger in cross section. Thus a spicule 2 micronsin width and 2 microns in breadth and 8 microns long would equalthirty-two cubic microns and occupy a space equal to eight ten-microncubes, or a cube 20 x 20 X 20 or eight thousand cubic microns. But insuch a cube it would have greater spacing. e. g. eighteen microns fromthe next similarly oriented (parallel) fiber on each side and twelvemicrons from the next similarly oriented fiber at each end. Hence itwould be freer and more likely to settle out of suspension, or de-water.This is the characteristic of water dispersions of longer or lessde-bered asbestos or other fibrous aggregates and suspensions.

On the other hand, if the ber size in cross section is the same asbefore, e. g. 1 micron x 1 micron, but the concentration is increasedsay to 2% by weight, increasing the length of each fiber, from fourmicrons to eight, then in the distribution above described the ends ofsuch spicules would approach one another to within four microns of eachother, while the sides will be at the same average space from each otheras before.

If the fibers remain 1 x 1 micron x 4 microns long and there are more ofthem, (e. g. 4% by weight in the suspension), so that there are say fourof them parallel and equally spaced laterally in the ten-micron cube offluid as supposed above, then they will be separated (by films of water)only four microns apart from each other and four microns from similarlyoriented parallel spicules in adjacent ten-micron cubes.

Of course if the spicules were to swell (laterally) they would stillfurther reduce this distance. Thus a 4% suspension of spicules is thelimit of the free working of paper or asbestos pulps, generally, upon alarge scale. And pulps of chrysotile asbestos (which does swell) assumea solid jelly formation at 4% to 6% concentration by weight. Hence, thefree working concentration of its pulp is about 1% by weight.

In other words, in an aqueous suspension of the preformed asbestos (orcellulose) fibers or spicules, the water films surrounding such fibers,for a depth of two to six microns, appear to be rmly adsorbed or held bythe fibers-and repel each other strongly, so as to produce and maintainthe uniform dispersion of the bers throughout the entire volume ofwater, in which they are suspended, even though the spiculated fibers donot swell.

The spiculated, dispersed fibers may hydrolyze and swell under Suchconditions, (or such hydrolyzing and swelling may be promoted), as withsome forms of asbestos, such as chrysotile asbestos, or with finelydivided organic ers, suoli as cellulose and its derivatives. This stillfurther promo es e dispersion and the permanency of such dispersions.But asbestos fibers of the prescribed dimensions, which do not swell, e.g. glilfailmhestgs" and African Amosite, will a so isperse in largevolumes of water,A and remain dispersed over substantial periods oftime, without spontaneous settling, and are also satisfactory for thepurposes of this invention. The criterion of the appropriate conditionof the fibrous material for the purposes of the present invention,appears, therefore, to be that the fibers shall present numerous freeends, shall be of nearly colloidal dimensions, in cross section, and ofsuf'iicient length to permit and promote free and uniform dispersionthroughout a volume of liquid upon being mixed therewith in diluteproportions (e. g. 1% to 5%) that they shall acquire and maintain arandom arrangement throughout the liquid or fluid mixture (in which suchfree ends are predominantly maintained spaced apart) and which inducethe incipient crystalformation at such separated points, thus to directtheir progressive crystal formation to a fibrous characteristic of habitor growth from such separated points, as distinguished fromcrystallization from closely contiguous solid surfaces or points, whichis the case in dispersions of finely divided powders in which all threedimensions of each particle are approximately the same.

It is to be particularly observed that the end faces of the pre-formedspiculated fibers, whether inorganic and crystalline or organic andnoncrystalline, present free, freshly fractured surfaces, asdistinguished from surfaces of natural and hence more stabilizedformations. They are, therefore, active as incipient centers for thecrystallization of the fibrous crystal-forming reagents in solution ordispersion. Since these free ends are of limited or even colloidaldimensions, the sizes of the (seed) crystals which they induce to formthereon are likewise limited. Extraneous crystal formation over thenatural side surfaces of the pre-formed fibers or crystals is notpromoted so much (if at all) as progressive crystallization when oncestarted, outwardly and radially from these fractured ends. Moreover, anycrystallization from the side walls of the fibers would be subject toadhesion, whereas the crystal growth from the end faces of thesefractured fibers involves cohesive forces or valence forces ofinteratomic combination.

While the ultimate formation of such preformed organic or inorganicfibers cannot be regarded as conclusive and certainly determined, it iscommonly accepted that finely divided organic bers, such as cellulose,which are commonly prepared, are made up of still finer and smallerentities, frequentlyreferred to as micelles, which are also of a fibrouscharacteristi, 'tHEt-'s':l being long in nmaisigwth'lross-sectionaldimensions. Likewise with inorganic or mineral fibers, such as asbestos,it is known that the fibrous masses as formed present a high order ofcleavage in two dimensions, resulting in the easy separation of the massinto long, fibrous crystalline needles. While the ultimate degree ofsuch separation which may be effected is not ascertained, it is knownthat it may be carried to an extremely small dimension, in bothtransverse directions. While the lengths of such fine fibers will alsobe unavoidably considerably reduced by fracture in such operations thefibrous characteristics will persist and can be effectively maintainedto present substantially greater lengths than the cross-sectionaldimensions, as above described.

An underlying cause of such fibrous characteristic of asbestos isattributed to the fact that the silicon and associated oxygen atoms arerelated and united in chain formation, longitudinally of the fibercrystals; Such union is of a primary valence order and consequentlyimparts considerable tensile strength to the fiber, longitudinally, incontrast tothe transverse weakness of union between the fibers. Upontransverse fracture of the individual (or ultimate) fibrous crystal,however, it is to be noted that a rupture is thereby effected in thesilicon-engen atomic chain of the crystal structure. Hence, thecorresponding cohesive or valence forces of silicon and oxygen whichhave constituted the longitudinal tensile strength of the fibrouscrystal are liberated and freed for physical or chemical union on thefractured face.

In the present invention, these fractured, and hence free, fiber-crystalfaces are greatly multiplied and dispersed through a large volume (ofwater) by spiculation as defined above, and hence constitute and providereactive centers of crystallization of an at least equal (or muchgreater) amount of the products of active lime and active silica (andwater) for the formation thereon, by chemical union and growththerefrom, of fine, needle-shaped or fibrous crystals of hydrous calciumsilicate. And it is the nature of such crystal growth, that the growingsilicate crystal will form a silicon-oxygen chain constituting a truecontinuation of the silicon-oxygen chain of the fine fiber-crystals ofspiculated asbestos, which have been severed by the spiculation. Theywill also be held apart in random arrangement, by the random arrangementof the long fine spicules and induced to form similar long fibrouscrystals themselves.

Consequently, the formation and growth of Asuch fibrous crystals fromthe ends of the preformed fiber spicules and their union therewith andwith one another, present an intergrown fibrous mass, the strength ofwhich is not measured by the adhesive strength of bonding materialsbetween themselves or between them and the pre-formed (organic orinorganic) fibers but by the integrated tensile strength of the cohesiveforces of the crystallized fiber structures themselves. For when twogrowing fibrous crystals meet and their intersection forms by mutualcrystallization from chemical reaction, the resulting product is aunitary formation of inherent cohesive chemical strength, and not one ofexternal contact, inclusion or adhesion.

For example, if the finely divided reactive silicon component abovementioned and dispersed or dissolved lime, as in lime water, aredispersed through a very large volume of water, and the particles (orsolution) retained in such wide state of dispersion with fine spiculatedfibers of asbestos, and the reaction therebetween to hydrated calciumsilicate is then effected, the needle-like crystals of hydrous calciumsilicate will be induced or compelled to grow longer and finer, andpresent a dispersed, entangled mass of fibrous crystals throughout theentire volume into which the reactive agents (and such points ofinception) have been held suspended during reaction. Moreover, thesegregating and forming crystals will, in

the course of their crystal growth, to a considerable degree unite atthe points of contact between two or more growing crystals and thusbecome intertwined and will form an interknit, open lattice of permanentarrangement and structure. Upon completion of the crystallization andgrowth 'of the crystals and subsequent removal of the :residual waterfrom between them, and from any water bearing gels between them (whichis in :fact observed to be the case) the mass will present innumerablevoids or air spaces, between the fibers, (and through the gel lms) whichare continuous and capillary in character and intercommunicating, ratherthan completely sur- -rounded or occluded, by a solid, such as thecontinuous bond or wall structures which are characteristic of andinherent in the structures of insulating materials of the prior art.

By employing a gel or voluminous disperse phase for the purpose ofmaintaining or promoting dispersal of the reagents and of the growingfibers, during the reaction, the reaction composition may be furtherpreserved of uniform consistency, composition and dispersion, and alsoretained in this condition for any necessary or suitable length of timeto effect completion of the reaction. At the same time, it may by slightagitation be subjected to free liquid flow, plastic :,ljl'ow, or thelike, whereby it may be transformed into any shape or dimensionsdesired. If the shaped mass is then held at rest, the mixture maybe'restored to gel condition and allowed to react or be subjected tosuitable conditions to initiate, promote and complete its reaction, forthe 'formation of the hydrated calcium silicate fibrous needles,throughout the entire charge, which con- 'sfequently conforms to theshapes, dimensions and volumes thus imposed upon it. The partially orcompletely developed crystalline mass may be subjected to modified oraltogether different treatments for special purposes and results. :Ihusit may be withdrawn from the shaping means and the reaction may becompleted by prolonged time, higher temperatures, pressures and Athelike, in a different container, with or without drying as the case maybe. Or, the development f the crystals and complete reaction of all the'ingredients of the entire charge may be effected in the originalshaping means before being withdrawn, if desired. In either case,residual moisture will finally be removed, in any convenient way, andthe moulded product is ready for use.

" The gel, whether formed in the reactions or added to the charge, mayor may not enter into the crystal-forming reaction. If it does,subsequent shaping or pouring of the mass may interrupt the crystalformation and consequently reduce the potential final strength of theproduct. If the gel is supplementary to the crystal-forming compositionand reaction, however, shaping and pouring of the gel mass may beeffected withut affecting the crystal formation structure and strengthof the crystallized product if it is carried 14 dimensions, in crosssection, and when the lime and silica have substantially completelyreacted the principal or, preferably, the only remaining ingredient ofthe mass of the charge is water or steam, both of which aresubstantially ultimately expelled, upon drying, and replaced by air.

When other materials or qualifications are provided in the reactivecharge, as above disclosed, e. g. to serve as a suspension medium orgel, or for other purposes, they may remain therein. Thus, finelydivided fibrouswellulosewsuch as paper pulp ,mayserve both as aspiculated fiber an asa gel. In this case the cellulose fibers, ofcourse, remain between the crystallized needles of hydrated calciumsilicate, even after the water and steam has been expelled. But thoughthe ce1- lulose fibers may add to the heat insulating properties of themass at room temperatures, they will tend to be reduced at thetemperature of boiling water or above, or the cellulose to be altered ordestroyed, as by charring and falling out of the spaces in which it haspreviously been retained. Such material would not, therefore, be asuitable permanent addition to heat insulating materials intended forvery high temperature service, though it would serve to promote thedisperse formation and dispersed crystallization of the hydrated calciumsilicate needles, in intermingled random fibrous formation, andintegrated as a mass, for medium or low temperature service.

On the other hand, it is found that by incorporating certain mineralsubstances, which are both fibrous and capable of undergoing gelformation and retaining their needle-like or fibrous form, such ascmhwrysotjglewasbbestos, a dispersed intra-knit structure offibrousiydrated calcium silicate crystals and fibrous asbestos crystalsmay be developed, constituting a fine continuous fibrous structure,throughout the mass, having an inter-knit integral relationship betweenboth kinds of fibers and the gel structure which is strong, of smallspecific volume and mass, resistant to high temperatures and of randomarrangement, consonant with the preservation of the fine, loose, opencharacteristics of the fibrous structure of the mass as a whole, andalso of the aggregate compressive and tensile strengths of both ultimateindividual fiber components, per se.

This fine fibrous structure of interlaced and intergrown brous crystalsis distinguished from the occlusive type of bonding, of fiber to fiber,by wetting, fusing, impregnating and/or like liquid bondings, orimpregnations, which are characteristic of the prior art. The laterdiffer from the intergrowth of fine crystalline fibers by presenting acontinuous, more consolidated structure, which is inherently of muchgreater apparent density, and also contains a larger volume of solid,contnuous structure from surface to surface of the same, through whichheat may be more readily conducted and dissipated and lost. At the sametime, since the voids or pore spaces of the fibrous mass produced by thepresent invention are not occluded or closed, the apertures between thebers and the solid crystals themselves and their junctions with oneanother are so attenuated and of such fine dimensions that orientedspaces, bodies, and surfaces for radiation and convection currents ofair through them are broken up and effectively dispersed and preventedfrom transferring heat progressively or rapidly through the mass as awhole, in any direction, by convection, by conduction, or by radiation.This system,'of continuous, illamentary, fine crystal formation and ofintervening continuous small attentuated capillary air spaces betweenand separating them, consequently presents a product which is as a wholeof low thermal conductivity and conversely of high insulating value, andyet possessed of high form-retaining value and tensile strength and verylow apparent density.

A representative example of the practical application of the inventionto the manufacture of heat-insulating materials, more especially of lowapparent density and low conductivity will be described, with referenceto the accompanying drawings, in which Fig. l is a diagrammatic flowsheet; and

Fig. 2 is a more or less diagrammatic illustration of suitable means forspiculating the asbestos fiber.

The asbestos component is preferably first prepared by reducing it fromthe crude state in which it is mined to an approximate degree ofuniformity and purity, relatively free from nonbrous minerals or otherimpurities. For example, the untreated asbestos may be composed oflchrysotlle asbestos fibers, sized as follows:

25% through a l" mesh and retained upon a 1A" mesh screen (Canadianasbestos specifications) 50% retained upon a 10 mesh screen 25% passinga 10 mesh screen This asbestos ber is then mixed with water as a liquidvehicle, in tank I, Fig. l. In carrying out this operation a relativelythick slurry may be effectively employed, as for example, by mixing 1 to5 parts of fiber by weight, with 99 to 95 parts of water to a uniformmixture by means of a stirrer 2. It is then draw off through pipe 3regulated by the valve 4 to the pump 5, whence it may be directedthrough outlet 6 through the pipe l and by opening valve 8, back intothe tank I, the valve 9 leading to the spiculating device I0, remainingclosed.

The spiculating device III comprises a motor I I (e. three-phase' type)adapted to drive shaft I2 which passes into the enclosed chamber I3 andcarries on its inner end a hardened steel conical disk I4 having radialutings I5 in its conical face I6, which is accurately and adjustablyspaced from a circular doctor blade I1, the surface of which is parallelto the surface of the conical disk I4 and held firmly in fixed position.The clearance between the conical disk and doctor blade is of the orderof .012 to .020". The disk I4 is preferably driven at a high speed ofrotation (e. g. 3600 R. P. M.) and preferably under constant maximumload, as indicated by the ammeter I8 (e. g. an operating reading of 70amps. on the motor used in the instant case) which is indicative of mosteffective spiculation of the throughput.

With the spiculating rotor at full speed, the valve 9 is now openedleading through the inlet pipe and into the chamber I9 which is on thecontrol or truncated side of the disk. Thereupon the slurry enters thechamber first under the impulse of the pump and thence under thecentrifugal force of the rotor and disk I4 which carries it into andthrough the clearance space between the face of the disk and the doctorblade. In this operation the asbestor fibers are twisted and opened upor separated from each other along their longitudinal planes of cleavageand also fractured and frayed or broomed transversely, resulting in agreatly multiplied number of discrete, separate brous entities at theirends which are in general characterized by small diameters (e. g. 116 to3 microns) in which the ratio of length to cross section characterizesthem as fibers, as distinguished from fine granules in which all threedimensions are substantially of the same order, and also from thatcategory of bers which are of such length as to introduce intertwiningand snarling or clotting, which is characteristic of unduly long fibersof untreated or non-spiculated asbestos.

As the slurry comes from the spiculator it is collected in the chamber20, whence it may pass into the educt 2| and thence through valve 22 andpipe 23 into a second tank 24, which is also equipped with a stirrer 25.

When all of the slurry prepared in tank I has been thus passed throughthe spiculator, and co1- lected in tank 24, the operation of the deviceis reversed. This is done by closing valves 4, 8 and 9 in the linesassociated with tank I and opening corresponding valve 26 in pipe 21,valve 28 in pipe 28, and later valve 30 opening into the inlet to thespiculating device l0; and also by opening valve 3| in pipe 32 leadingfrom the spiculator outlet 2| back into the tank I, all of which havepreviously been closed.

By now operating the pump and spiculating device as before, the batch ofslurry will be given a second treatment or pass, similar to the rst. andthen discharged into the tank I, until the entire charge has been thustreated a second time.

These operations may be thus reversed and repeated as many times as maybe regarded to be necessary or desirable. But for effective red uctionof the bers to a suitable degree for the purpose, two or three passesoften have proven sumcient.

When the slurry has acquired the desired degree of spiculation all ofthe foregoing valves are closed except the valve (4 or 26) in the pipeline leading from the tank containing the finished batch of spiculatedasbestor slurry, to the pump 5, and the valve 33 which leads from theoutlet of the pump through pipe 34 to the mixing tank 35 is opened.Operation of the pump I will then deliver the entire batch into themixer 35.

The mixer 35 is a usual type of horizontal cylinder, with a pair ofoppositely pitched helical. ribbon-shaped mixing blades.

Previous to the introduction of the prepared asbestor slurry into themixer, a suspension of finely pulverized quicklime (e. g. mesh andfiner) is hydrate w1 wa r which is at room temperature and in suiliclentquantity to provide a freely fluid suspension preferably at atemperature of 16o-200 F. The amount of water employed is such as toproduce a composition in the mixer of the desired consistency,dispersion and suspension. For example, five times as much water asquicklime, by weight, will produce effective slaking, dispersion, and asatisfactory resulting slurry. When the lime is completely hydrated anddispersed in the water in the mixer, the Ls lnunrry of s iculategasbestos fibers is pumped in, mixed thoroug y, an e requ ite amount offinely divided i l i diatomaceous earth or the like is added in finelypow ere ry con tion,

and the mixing continued until complete and uniform dispersion of theentire batch is effected.

Typical and representative examples of compositions, which may beprepared in accordance 17 with the procedure of the invention are asfollows: I

Lime, 30% by weight, e. g. 30 lbs. Diatomaceous earth, 50% by weight, e.g. 50 lbs. Asbestos (as prepared in apparatus of Figure 2),

20% by weight, e. g. 20 lbs.

Water with asbestos, 400% of total weight of solids, e. g. 400 lbs. (orto 470 lbs.) i Water with lime, 150% of total weight of solids, e. g.150 lbs. (or to 130 lbs.)

III

Lime, 30% by Weight, e. g. 30 lbs. Diatomaceous earth, 50% by weight, e.g. 50 lbs. Asbestos (as prepared in apparatus shown in Figure 2), 20% byweight, e. g. 20 lbs.

Water with asbestos, 850% of total weight of solids, e. g. 850 lbs. gWater with lime, 150% of total weight of solids, g e. g. 150 lbs. i f.IV

Lime, 33% by weight, e. g. 33 lbs. Quartz flour, 60% by weight, e. g. 60lbs. J Asbestos (completely spiculated, e. g. dry, in air suspension, 7%by weight, e. g. 7 lbs.

Water with lime, 150% of total weight of solids, e. g. 150 lbs. .fWater, 100% of total weight of solids, e. g. 100 lbs. The mixingoperation usually requires from 30 minutes to an hour. When complete,the mixing is stopped and the slurry is withdrawn, and may be owed bygravity into metal moulds or pans 36 or similar containers, which areApreferably thin and good conductors of heat, which are then placed in achamber 31 and subjected to live, saturated steam at 120 lbs. pressure,e. g. three hours to bring the chargeuptotenperature, held for a periodof twelve hours at constant pressure and allowed to cool and thepressure to fall to that of the atmosphere over a period of iive hoursmore or less. They may then be withdrawn or allowed to cool further. Themoulded charge will be found to have become indurated in its originalsize and shape without appreciable separation of water, nor shrinkagefrom its original size and shape.

The moulded product may therefore be removed from the pans, and thecontained water removed by drying at 250350 F. leaving a producthavirgtheshape-and-dimensions irnparted to it by the moulds, and aweight equal to that or the solid components of the reaction mixtureonly (plus the combined water of crystallization and absorbed moisture.and absorbed water, if present) and from which the water of dispersionhas been removed, and which is of low apparent density accordingly..

For example, such a product (e. g. of Formula II) manifests an apparentdensity of about eleven pounds per cubic foot and having a conductivityof approximately -.0002 at hot side temperatures up to l200 F. if thecold side is at 18 about 150 F. This apparent density may be controlledin terms of the concentration of solids in the original slurry fromwhich it was prepared and which was indurated. And since there is noappreciable volume change in the process the product will havesubstantially the same apparent density in pounds per cubic foot thatthe original slurry contained in terms of its solid components (pluswater of crystallization and/or otherwise bound water), the voids in theone case being filled with liquid water and in the other case with air.

Obviously other products may be produced. by preparing slurries ofspiculated asbestos, in which its markedly prolonged or permanentsuspending powers may be utilized, for many purposes. Thus, it may serveto eiect and maintain the dispersion of much heavier materials or largerproportions of reagents, during reaction or other treatments, whetherthe product is to be of low or high apparent density.

In this invention both the degree of spiculation and the proportion ofshort to long fibers are controlled and in turn determine the propertieswhich are desired in the product. In this respect the present inventiondiffers fundamentally from other attempts in the art.

For example, in the production of high density structural materials,more densely populated with solid cementitious reagent materials andduction of low density products, designed to serve as a form-retainingheat insulation product, comparatively sparsely populated with solidcementitious reagent materials and reaction products, the partiallyspiculated asbestos of the order (C) as dened above has been found toimpart relatively high fiexural strength, in comparison with lowapparent density products of the prior art, and also high residualstrength after initial fracture of the cementitious bond.

The spiculated asbestos may be produced from commercial grades ofasbestos by treating a suspension of such asbestos in a fluid (eithergaseous or liquid) in an instrument or apparatus which subdivides thefibers by the action of attrition or the cyclonic vortex of the fluidrevolving at high angular velocities. Such disintegration can beaccomplished by various mills designed to operate using compressed air,or high pressure superheated steam as the iluid medium, or it may beaccomplished by agitating a dilute suspension of about 5% more or lessby weight (1% to 10%) of asbestos in water by means of one or more highspeed propeller agitators, or it may be accomplished by beating such asuspension in a paper pulp beater. But in each oi these operations, thetreatment is conducted to a much more intensive degree and is prolongedmuch beyond that ordinarily employed in such procedures and equipmentfor the preparation of the pulps which they are primarily designed toprepare, in order to effect the required degree of reduction of thefiber size and the required proportion of the brous material to thatsize or sizes characterizing spiculated asbestos. Thus completelyspiculated asbestos iiber may be produced by prolonged or repeatedtreatment, in the apparatus shown, of a 1% suspension by weight. The netresult of such treatments is to disintegrate the bundles oi' spicules orfiber content of the commercial grades of asbestos into substantiallytheir ultimate spicules, but without destroying their iibrouscharacteristics of length relative to their cross-sectional dimensions.

Consonant with the present disclosure, the spiculated fibers or spiculesare characterized by being capable of forming a relatively permanent orstatic suspension in water, e. g. which are in concentrations of l;o% to2.5% (or more) by weight or 1;5% to 1% by volume (or more) are, per se,resistant to segregation by gravity for a period of several hours (oreven for days).

Such static dispersion and prolonged suspension of ne spiculated berstherefore constitute a disperse system in which numerous uniqueconditions and characteristically novel reactions and results may beattained.

'Ihus other fibrous materials, or granular materials, or ilnely dividedsolid reagent materials (or in solution) which are not capable ofprolonged suspension in liquids may be mingled with them, and theresulting mixture will acquire this capacity for forming and maintaininga uniform, prolonged or permanent static suspension, without appreciablesegregation, for a substantial period of time. Accordingly, variousreactions and other changes may be eiiected throughout suchthree-dimensional suspensions and successively controlled to denitedegrees of (1) initiating such reaction. (2) promoting or controlling itto any desired stage, or (3) carrying it to completion. Moreover, otherprocedures may accompany or intervene between these successive stages ofphysical and/or chemical reaction in the system, such as shaping ormolding the mass before initiating the reaction, afterinitiatlng thereaction or after promoting the reaction to any desired degree.Moreover, subsequent treatments may be eilected upon the resultingmixture at any selected stage of operation, according to thecharacteristics of conditions and properties thus acquired and accordingto the ultimate changes and results desired.

Thus. for example, in the speciilc examples described above, byemploying reactive lime and a reactive silica (slightly in excess ofequimolecular proportions) and carrying the reaction to substantialcompletion, a new atedliInesilicate having the composition Ca0.Si .n 2ys orme which upon examination exlbits a novel X-ray pattern,distinguishing it from all of the known silicates of lime.

It is believed that in the static. continuous, but open nlamentarynetwork of suspended spicules, which are characteristically capable ofsustaining themselves in suchl arrangement and dispersion throughout thevolume of water in which such network is formed, numerous reagentmaterials, both in solution and in the form of solids of small andcomparatively large dimensions, are rendered susceptible to controlledreaction. both chemically and physically.

Thus, in the charges above described, the lime is present both insolution and in colloidal to visible particle sizes. 'I'he silica islikewise present in iine sizes, either as quartz flour or as powdereddiatomaceous earth, though particles of the latter may be considerablylarger than the f1- brous spicules. The silica also is capable of goinginto'solution. Hence, reaction between dissolved lime and dissolvedsilica may be predicated. Moreover, owing to the porosity orpermeability and also the amorphous Vand active character of the silicaof the diatomaceous earth, the lime solution and suspension is capableof penetrating additional crystalline calcium silicate.

the large particles of diatomaceous earth relatively freely.Furthermore, under such conditions, the dissolved lime is capable ofreacting with manyiseg `35 times) its" molecular quivalent'of 'silica'and dispersing or dissolving tlirsultirig combination in the surroundingaqueous medium. Such a combination may be postulated or visualized as along chain of silicon and oxygen, combined at its ends to one moleculeof lime.

Such action will obviously quickly and completely disintegrate andmomentarily at least, dissolve the silica or diatomaceous earth, all outof proportion to the (equi) -molecular quantity of lime present. But theconcentration of such lime-silica combination which can be retained insolution is rather small. It is competent to reorient itself, and in sodoing fibrous crystals of lime silicate of the formula CaO-SiOz'nHzOseparate out and grow, as above described, distributed throughout thevolume of the reactive mass. The silicon-oxygen, or silica chains thusliberated may in turn react with more lime to form lime silicates ofvarying compositions, or Such silica chains or lime silicates tend alsoto go over to gel formations, distributed throughout the mass. These inturn may progressively, and rapidly or slowly according to conditions,be converted into and thus feed the growing fibrous crystallinestructures above described. Upon such crystal formation being arrested,however, the gel structure will remain. Thus, if the water medium isremoved, such crystalline growth of fibers may be stopped, and heat anddehydration serve to collapse the gel structure upon the preformedfibrous spicules, the growing fibrous crystals, and within themselves,thus opening up voids between the bers and creating continuous and hencepermeable openings through the gel itself so as to produce the typicalstructure of the novel product obtained.

' Further h atln dr ing, and dehydrating of the spicuiesstagst'ry'sms,massacrare is accompanied by a shrinkage in absolute volume, hardening,and strengthening of each, and also of the union between them, toconstitute the integral, form-retaining and strong structure,characteristic of the whole, which has not been secured in the processesand insulation materials of the prior art.

All of the modications and adaptations, both of the underlyingprinciples and of the practical applications of my invention, which maybe made within or derived from the purview and scope of my disclosureare intended to be constructed as contemplated and as claimed herein.

The foregoing constitutes the specification of v associated with thatber that the fiber and water act as an entity. They will attract and,A

repel a similar ber and its associated water suiliciently to eiect andmaintain this evenly spaced relationship against the forces of gravity,

[trite s x i i.

andere whether of buoyancy or of settling. But if such a suspension befurther sharply diluted with water, the suspension breaks, the fibersfloat to the top, leaving clear water below, and forming a top layercomprising a suspension of approximately the original limitconcentration -before such dilution (or a slightly greaterconcentration) which floats on the lower water layer.

Therefore this degree of dilution indicates the limit of the thicknessof the water envelope about the fibers which iseffective to keep eachfiber apart from adjacent fibers and also to prevent free movement ofone fiber past or against the other, such association of water toadjacent fibers also prevents free circulation of water between suchadjacent fibers, so as to cause segregation by settling or floating. Onthe other hand the water envelope is not sufliclently firmly associatedwith its fibers to prevent it from being readily filtered or drained outof the fibrous mass, and thus letting the fibers come together. In otherwords the system is a discontinuous suspension of fibers, which isstable and permanent so long as the water medium is maintained, but itis not a gel nor a continuous gel, even with chrysotile fibers whichswell somewhat.

In this open, three-dimensional fibrous network or lattice system,therefore, the reagent materials, as finely divided solids or incolloidal or true solution, are capable of dispersion, withoutdestroying the lattice structure or suspension. Both lime anddiatomaceous earth for example are capable ofsuch subdivision tocolloidal dimensions and of going into true solution. When or in so faras the reagents are present in the latter conditions they react rapidlyand produce a dilute gelatinous precipitate of hydrous calcium silicate.Owing to the dispersed, dilute character of this gelatinousprecipitate,- it is mobile and is attracted to the spiculated asbestosiibers. It freely conforms to the outer surfaces of the fibers, formingaround each of them a sheath of gelatinous hydrous calcium silicate.This sheath therefore surrounds each of the fibers, within the envelopeof water which was associated with and surrounded each of these fibersand which still none the less continues to be effective to maintain thehydrous calcium silicate gel coated fibers in their widely spaceddispersed relationships.

Therefore, the dissolved reagents permeate the water envelope of thesefibers and a gelatinous precipitate builds up directly upon each fiber,without a'ecting or destroying the separating envelopes of water abouteach asbestos fiber. The

latter are therefore continuously maintained in their original spacedrelationships and continue to occupy their same volume and shape, in theoriginal network or lattice system which they formed in the waterdispersion alone.

Such reactions of dissolution and combination of the lime and silica, e.g., in the form of diatomaceous earth, proceed at ordinary temperatures.If the temperature is raised, the reactions are accelerated, theformation of crystalline hydrous calcium silicate also takes place,either by direct crystallization from solution or by conversion of thegelatinous precipitate to a gel, ultimately to develop prominentcrystalline forms. But the crystalline formations of the invention havebeen described in detail above.

Such dissolution, reactions and precipitation of the reagent materials,and selective deposition of gelatinous precipitates may also take placeindependently of the fibers and form clots or co1- onies of gels andcrystals throughout the volume of the mass and yet not interfere withthe maintenance of the dispersion of the spiculated fibers, asoriginally set up in pure water. Hence the gelatinous sheaths of hydrouscalcium silicate surround and grow out from the continuously dispersedspiculated fibers of asbestos and clumps of gelatinous precipitate ofhydrous calcium silicate also simultaneously form independent of andspaced from the fibers in the aqueous medium.

Crystals of hydrous calcium silicate may form directly from solutionand/or further crystallization may take place by conversion of thegelatinous precipitate to crystalline form. But the gelatinousprecipitates, especially on the bers tend to consolidate to gels, ofgreater cohesive and adhesive strength, lower volume, and greaterdensity than the original gelatinous precipitates.

In so doing they coalesce about the fibers and then contract andcommensurately leave increasing spaces of open water between one suchfiber and the next, since the fibers themselves neither when bare norwhen coated with the gelatinous or gel-like sheaths, manifest anytendency to come together into direct contact so long as a sufficientrelative volume of the aqueous medium is maintained about and betweenthem.

Accordingly the charge as a whole, consists initially of dispersedspiculated fibers with subsequently intermingled finely divided lime anddiatomaceous earth, in finely divided form, colloif dal suspension andin solution. Reaction produces discrete gelatinous precipitates whichaccumulate about the spaced fibers, forming an enclosing sheath abouteach, and also dispersed gelatinous precipitates, in colonies which areinindependent of the fibers. These gelatinous precipitates may be ofsilica or lime or of hydrous calcium silicate. They form at ordinarytemperatures and grow larger with time and with increased temperatures.At elevated temperatures crystals of hydrous calcium silicate also form,throughout the mass, both from solution and from the gelatinousprecipitates. They form on the fibers and are also spaced from thefibers. Throughout such reactions and growths, the fibers maintain theiroriginal spaced relationships, and accordingly, as the gelatinousprecipitates consolidate about their respective fibers and the crystalsseparate likewise, from the intervening spaces, the latter remainoccupied by water alone.

When such reactions are complete, the water is allowed to vaporize andescape. The residual gelatinous precipitates or gel-sheaths about thefibers (which have already shrunk to true gels) then acquire a porousstructure, then submi croscopic crystal formations, and develop greatercohesive, adhesive and total strength, accord ingly.

The independent clots or colonies of gelatinous precipitates, which formbetween and independent of the fibers do not wet the fibers with aspreading meniscus. But they do contact them ultimately (with loss ofthe dispersing water which maintains them separate) in theform-retaining masses which become substantially onedimensional bers asthey adhere and continue to shrink, upon dehydration, to stiff gels. The

gel-like sheaths of the spiculated fibers and the precipitated gelfibers thus formed may or may not be crystallized by subsequenttreatment, but in either case they reinforce the crystalline formsgenerated by direct separation from solution be- 23 tween the spiculeswhich are described in the foregoing specification, and constitute anintegrated network and solidiiied structure.

The whole mass thus ultimately becomes an integral, open, brous mass oflight-weight, lowheat conductivity, high tensile strength, and isresistant to both water and high temperatures. making it suitable as ashaped, self-sustaining low-apparent density heat insulation material,suitable and satisfactory for use at high temperatures, and for makingcomplete heat insulating installations, of one composition and in onepiece.

I claim:

1. The method oi making a light weight open iibrous structure comprisingforming a stable dispersion in water spiculated bres selected from thegroup consisting of asbestos and cellulose fibres, lime and nely dividedsilica, the lime being present in proportion to spiculated libres of atleast about 1.5 to 1 by Weight, and the silica being present in not lessthan equi-molecular proportions of the lime, said spiculated iibresbeing predominantly of cross-sectional dimensions from about one-tenthto three microns and Of lengths which are at least about three timestheir respective cross-sectional dimensions and being from about 1/zs%to not greater than about 5% by volume of the water, reacting said limeand silica by heating the mixture while preventing substantial loss ofwater to form a solid, hydrous, lime silicate, said dispersion retainingits stability during the reaction and said spiculated fibres andreaction product forming an integrated structure having substantiallythe volume and shape of the dispersion and which volume and shape aresubstantially retained upon dewatering.

2. A form-retaining product characterized by being of a continuous,open, brous structure composed of spaced, randomly dispersed, spiculatedbres selected from the group consisting of asbestos and cellulose fibreswhich are predominantly of ,cross-sectional dimensions from onetenth tothree microns and of lengths which are at least three times theirrespective cross-sectional dimensions, bonded with a solid, hydrous,lime silicate, said product being prepared by the method of claim 1.

x 3. The method according to claim 1 wherein 4. The method according toclaim 3 wherein a relatively small amount of unspiculated asbestosfibres are also present in the dispersion in water.

5. The method according to claim 1 wherein /the spiculated bres areasbestos fibres.

hydrous lime silicate is formed as crystalline bres.

6. The method of making a light weight, open brous structure comprisingforming a stable dispei-sion in water of spiculated iibres selected fromthe group consisting of asbestos and cellulose bres, lime and finelydivided silica, the lime being present in proportion to spiculated bresof at least about 1.5 to 1 by weight, and the silica being present insuillcient amount to convert substantially all of the lime into hydrouscalcium silicate, said spiculated ilbres being predominantly ofcross-sectional dimensions from about one-tenth to three microns and oflengths which are at least about three times their respectivecross-sectional dimensions and being from about j/25% to not greaterthan about 5% by volume of the water, reacting said lime and silica byheating the mixture while preventing substantial loss of water to form asolid, hydrous, lime silicate, said dispersion retaining its stabilityduring the reaction and said spiculated fibres and reaction productforming an integrated structure having substantially the volume andshape of the dispersion and which volume and shape are substantiallyretained upon dewatering.

7. A form-retaining product characterized by being of a continuous,open, brous structure composed of spaced, randomly dispersed, spiculatedfibres selected from the group consisting of asbestos and cellulose breswhich are predominantly of cross-sectional dimensions from onetenth tothree microns and of lengths which are at least three times theirrespective cross-sectional dimensions, bonded with a solid, hydrous,

lime silicate, said product being prepared by the method of claim 6.

LEWIS H. D. FRASER.

REFERENCES CITED The following references are of record in the ille ofthis patent:

UNITED STATES PATENTS Great Britain 1939

